Evolution of a 3 msun star from the main sequence to the ZZ Ceti stage the role played by e
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The evolution of starsStars are the most noticeable objects in the vast universe except the sun, moon and a few planets. In ancient times, people were full of curiosity and fantasy about stars, and very moving myths and legends were popular in China and abroad. However, it was not until the telescope appeared that people had the most basic understanding of stars and realized that stars were not constant in the sky.At the beginning of the20th century, Einstein published the famous mass-energy relationship, people gradually realized the huge energy produced by the nuclear reaction and knew the source of the star's energy before they gradually realized that the star itself also had a life cycle, they would be born, grow, and die just like people. However, the birth of stars was still a mystery for a long time. It was not until the 1960s that astronomers discovered molecular gas in interstellar space that they had the most preliminary understanding of the evolution process of stars. Next, I’d like to share it. Gravitational contraction stageThe star was originally born from interstellar dust in space. Scientists call it "nebula" or " interstellar cloud" vividly. Its main component is hydrogen, which is extremely small indensity but huge in volume and mass. The nebula with enough density continuously shrinks and its temperature rises under the action of its own gravity.When the temperature reaches 10 million degrees, a thermonuclear fusion reaction takes place inside it, releasing a large amount of atomic energy and forming radiation pressure, when the pressure increases enough to compete with the gravitational pull of its contraction, a star is born.Main sequence starThe stage in which a star uses internal hydrogen and helium fusion as its main energy source is the main sequence stage of the star, which is the ‘youth” of the star. It is the longest golden stage in the life of the star and occupies 90 % of its entire life span.During this period of time, the star is relatively stable, the two forces of outward expansion and inward contraction are roughly balanced. The star does not shrink or expand basically, and emits heat with almost constant luminosity, illuminating the surrounding space.The time that different stars stay in the main sequence stage varies greatly with different masses.The greater the mass, the greater the luminosity, the faster the energy consumption, and the shorter the time spent in the mainsequence stage.Stars whose mass is equal to 15, 5, 1, and 0.2 times the mass of the sun are in the main sequence stage for 10 million years, 70 million years, 10 billion years, and 1 trillion years respectively.Red giant star stageWhen a star passes through its long main sequence stage, it will first become a red giant star.Because the burning consumption of hydrogen in thermonuclear reactions increases, the rate of helium formation will continue to increase.Soon, the hydrogen around the helium core will become very small, and the energy generated by the central core will no longer be sufficient to maintain its radiation pressure, so the balance will be broken and the gravitational force will be greater than the radiation pressure. After that, the process of star evolution is that the inner core shrinks and the outer shell expands. At the same time, the outer shell of the star expands outward and keeps getting cold, and the surface temperature is greatly reduced. The process only lasts hundreds of thousands of years, and the star becomes a red giant in rapid expansion.Because the volume will expand to 1 billion times and is very huge, it is called "superstar".While the star isexpanding rapidly, its outer surface is getting farther and farther away from the center, its mass is easy to lose and its temperature is getting lower and lower, and the emitted light is getting redder and redder, so it is called a "red" giant star. Because of its huge volume, its luminosity has also become very large, extremely bright. Many of the brightest stars visible to the naked eye are red giant stars.Outbreak stageThe stars in their later years are very unstable. One day they will explode violently. By then, the whole star will have formed its own life with an extremely spectacular explosion, throwing most of its material into the sky, turning it into a nebula again, and releasing huge energy at the same time. In this way, in just a few days, its luminosity is likely to increase by several hundred thousand times. This kind of star is called "nova". If the stellar explosion is more violent, its luminosity can even increase by more than 1,000,000 times or even 10,000 times. This kind of star is called "supernova." The explosion of new stars or supernovae is an important link in the evolution of celestial bodies. It is the brilliant funeral of old stars and also the promoter of the birth of new stars. Theexplosion of supernovae may lead to the birth of countless stars in nearby nebulae.High density stageAfter the explosion, the supernova left only ahigh-density debris, instead of a star.Stars with a mass below 1 - 3 times the mass of the sun lose enough mass without drastic changes after leaving the main star sequence belt, and end their lives relatively peacefully and become a white dwarf.Stars with 3 times the mass of the sun will end up in supernova explosions. Within seconds of the explosion, the core will begin to collapse and eventually collapse into dense neutron stars.The mass of neutron stars is not infinite.If the core residual mass still exceeds about three times the mass of the sun after the supernova explosion, the central portion will continue to shrink.Finally, when the mass shrinks to a very small extent, the gravitational force near it is large enough to make the fastest moving light unable to get rid of its confinement.This celestial body cannot send any information to the outside world, which is called a black hole.In this way, stars come to the nebula and return to the nebula, completing its glorious life.。
The universe is a vast expanse that has fascinated human beings for centuries.It is the collection of all existing matter and energy,including galaxies,stars,planets,and other celestial bodies.Here is a detailed introduction to the universe in an English essay format.Title:The Enigma of the UniverseIntroduction:The universe,a boundless and aweinspiring concept,has been a subject of wonder and study for as long as humanity has gazed upon the stars.It is the ultimate frontier,a testament to the infinite possibilities that lie beyond our terrestrial realm.Composition of the Universe:The universe is composed of billions of galaxies,each containing billions of stars.Our own galaxy,the Milky Way,is just one of these celestial bodies.Surrounding these stars are planets,some of which,like our Earth,are capable of supporting life.The universe also contains vast amounts of dark matter and dark energy,which,despite being invisible, play a crucial role in the expansion and structure of the cosmos.The Big Bang Theory:The most widely accepted explanation for the origin of the universe is the Big Bang Theory.According to this theory,the universe began as an infinitely dense and hot point, and has been expanding ever since.This event occurred approximately13.8billion years ago and set in motion the creation of all the matter and energy that we observe today.Galaxies and Stars:Galaxies are massive collections of stars,gas,and dust held together by gravity.They come in various shapes and sizes,from spiral galaxies like the Milky Way to elliptical galaxies that are more rounded.Stars,the powerhouses of galaxies,are born in nebulae and can live for billions of years,undergoing various stages of evolution before they die, sometimes in spectacular supernova explosions.Planets and Solar Systems:Planets are celestial bodies that orbit stars.They are diverse in nature,ranging from rocky terrestrial planets like Earth to gas giants like Jupiter.Our solar system,with its eight planets,is just one example of the many solar systems that exist within galaxies.Life in the Universe:The search for extraterrestrial life is an ongoing endeavor.While Earth is the only known planet to harbor life,the vastness of the universe suggests that the conditions necessaryfor life could exist elsewhere.Scientists are continually searching for signs of life on other planets,moons,and even in the interstellar medium.The Expansion and Fate of the Universe:The universe is not static it is in a state of constant expansion.This expansion is driven by dark energy,a mysterious force that is causing the universe to stretch at an accelerating rate.The ultimate fate of the universe is still a topic of debate among cosmologists,with possibilities ranging from a Big Freeze to a Big Rip.Conclusion:The universe is a complex and dynamic entity that continues to reveal its secrets to us.As our understanding of the cosmos grows,so too does our appreciation for the intricate balance of forces that govern its existence.The universe is a reminder of our place in the grand scheme of things and the boundless potential for discovery that lies ahead. Further Exploration:The study of the universe is a collaborative effort that spans disciplines and cultures. From the earliest stargazers to modern astronomers and astrophysicists,the quest to understand the universe is a testament to human curiosity and our desire to explore the unknown.As technology advances,we can expect to uncover even more about the cosmos and our place within it.。
My name is Captain James Tiberius Kirk. 我叫詹姆士·提比略·柯克United Federation of Planets 来自星际联邦I came here before you as a neutral representative 我此次前来的目的是作为of the Fabonane Republic. 法博南共和国的中立代表And bring you a message of good will 为特纳科斯星代表团各位尊敬的成员And present to you, esteemed members of the teenaxienedelegation带来法博南共和国议会诚心的问候A gift from Fabonan High Council with the highestregard.并献上这份充满诚意的礼物What's wrong with it? 这东西是坏了吗- Excuse me? - Why the don't they want it anymore? -什么-那他们为什么不想要了Well... This was once a piece of an ancient weapon 这曾是一件上古兵器的碎片and now they offer it as a symbol, of... 现在他们送来是想作为和平的... ... of peace. 象征In the Fabonan culture this surrendal weapon 在法博南的文化中献上投降武器is an offer of truce. 代表休战How they got it? 他们怎么弄来的They told me, they acquired it long time ago. 他们告诉我是很久以前拿到的So they stole it, then! 也就是偷的了No... the uhm... 不... 这...Y ou don't know the Fabonan like we do ! 你可没有我们了解法博南人That's very true. Y our excellency, this gift... 的确如此大使阁下但这件礼物...They are crowds of untrustworthy thieves. 他们是一群不值得信任的窃贼who wants to see us murdered in our own base. 就想看我们在自己家里被屠杀This beloved artifact is a symbol of trust and peace. 这份礼物是信任和和平的象征They will cut us into pieces, and roast us over a fire... 他们会把我们碎尸万段然后架在火上烤I don't think that's true... 我不太同意这个观点...... and eat us !! 然后吃了我们What ?! 什么Scotty!! Get me out of here! 小科快把我弄出去Well, that was quick. 这么快就搞定了There is quite a bit a surface interference, sir. 长官你身体表面的信号干扰很严重Scotty! 快点I ripped my shirt again. 我又把衣服弄破了How'd it go? 进展如何Captain, did you manage to broke a treaty with the Teenaxi? 舰长您跟特纳科斯人达成协议了吗Uhm... Let's just say we came up short. 算是功亏一篑吧... Would you... lock that back 你能不能... 把那东西into the personal vault, Spock. Thank you. 锁回保险箱里去斯波克谢谢- Jim, you look like crap. - Thank you, Bones. -吉姆你样子糟透了-多谢夸奖老骨头Y ou have a little vein popin out of your tremble again.Y ou okay?你太阳穴又青筋暴起了你还好吗Never better. It's just a another day in fleet. 好得不得了又在星际舰队度过了美好一天Captain's Log, Stardate 2263.2 舰长日志星历2263.2年Today is our 966-day in deep space. 今天是我们在深空的第966天A little under 3 years of our 5 year mission. 我们的五年任务已经过了快三年More time you spend out here, the harder it is 在深空中待的时间越长to tell where one day ends and the next one begins. 要分辨一天的始末就越难It can be a challenge to feel grounded 这种被囚禁的感觉算是个挑战where even gravity is artifical.毕竟这儿连重力都是人造的But while we do what we can to make it feel like home. 但我们会尽力让一切有家的感觉The crew is always continues to act admirably 船员们持续着出色的表现despite the rigors of our extended stay here in outer space 无论在外太空的长期停留有多艰苦and the personal sacrifices they have made. 或个人为此做出了多少牺牲We continue to search for new life forms in order 我们继续搜索新的生命形式to establish firm diplomatic ties. 以便建立牢固的外交纽带Understanding the time in uncharted territories 在未标记的星际领域的时间stretched the ship's mechanical capacities 耗损了飞船的机械性能but fortunately, our engineering departement led by Mr. Scott 但幸运的是由斯科特先生带领的工程部...is more than up for the job. 应付起来绰绰有余The ship aside, prolonged cohabitation has... 另一方面飞船上长期的共栖生活definitely infects on interpersonal dynamics. 无疑对人际关系产生了影响Some experience is for better... 有的关系会更好...and some for the worse. 也有的会更糟As for me things have started to feel little episodic. 对我来说生活也开始变得周而复始Further out we go, the more I find myself wondering 我们走得越远我就越开始疑惑what is it we are trying to accomplish. 我们到底想实现什么If the universe is trully endless, then... 如果宇宙真的无尽那我们怎么知道......if we're not striving for something forever out of reach. 我们是不是永远达不到目标The Enterprise is scheduled for repermission to stop atY orktown,进取号计划申请停驻约克镇Federation's newest and most advanced starbase. 星际联邦最新最先进的星际基地Perhaps a break from routine will offer us some rest, but... 也许暂时摆脱既定日程能让我们稍作休息...from mysteries, the unknown. 从神秘和未知中抽身片刻Sorry, I'm late. 抱歉我来晚了Keenser's leaking some kinda highly acid green flu... 金瑟一直在流一种绿色高腐蚀性酸鼻涕......and Scotty is terrified, he's gonna sneeze on warp core 小科吓坏了怕他会在曲速核心上打喷嚏and kill us all. 把我们都弄死What the hell are you drink? 你喝的是什么鬼Pretty sure it's the rest 应该是我们在赛瑟斯of that Saurian brandy we picked up on Thasus. 捡的那瓶蜥蜴白兰地还剩了一点My god man! Are you trying to go blind? 天你是想把自己弄瞎吗That stuff's illegal.那东西是违法的Besides, I found this in Chekov's locker. 而且我在切科夫的柜子里发现了这个没想到吧我一直以为他喜欢伏... Right, I mean I always assumed he would be V odkaguy...V odka guy. Exactly. 伏特加就是我想给你准备个像样的生日礼物I wanted to have something appropriate for yourbirthday.It's in a couple of days, you know I don't care about that. 还有好几天呢而且你知道我不在乎I know. Y ou don't like celebrating it on the day... 我知道你一直不喜欢在当天庆祝...because it's also the day your pop bit to dust. 因为那天也是你父亲化作星尘的日子I was being sensitive.我在尽力感性一点医学院没教你怎么好好说话吗Did they teach you about bedside manner in medicalschool?Or it's just your southern charm? 或者你们南方佬就这特点- Oh yeah. Ooh. That's good. - Lordy. -太棒了-老天爷Y ou're gonna call your mom? 你会打给你妈吗Y eah, of course I'll call on the day. 当然生日那天我会打的I'm one year older. 我又老了一岁Y eah, that's usually how it works. 生日就是这个意思A year older than he ever got to be. 比他去世时的年纪还大一岁He joined the Starfleet because he... 他加入星际舰队是因为他... ...he believed in it.他相信这一切I joined on a dare. 而我跟人打赌加入的Y ou joined this to see if you can live up to him. 你加入是为了不辜负他It's been all this time, you are trying to be George Kirk... 长久以来你都努力活得像你爸现在你想知道做回自己意味着什么...and now you're wondering just what it means to beJim......why you're out here. 想知道你为何仍在这里To perfect eye sight and a full head of hair. 祝你有完美的视力和一头茂密秀发- Kirk here. - Captain. -我是柯克-舰长- Approaching Y orktown base. - I'm on my way, Mr. Sulu. -正接近约克镇基地-马上来苏鲁先生Let's keep this birthday thing under wraps. 生日这事替我保密Y ou know me. Mr. Sensitive. 你知道我的感性先生Woaah, that is impressive. 太壮观了A y. She is a beauty, isn't she? 真美啊是吧What a damn monstrosity. 好一个深空怪物Can't we just rent some space on a planet? 我们就不能在某个星球租个地方就算吗Showing geographical favouritism 在已加入星际联邦的星球中among conducted Federation worlds 表达地理偏好could cause diplomatic tension. 可能会导致外交紧张Oh, you don't think that looks tense? 难道那东西看起来就不紧张吗Looks like a damn snow globe in space just waiting to break. 就像太空中的一个雪球等着被打碎呢Ah, that's the spirit, Bones! 精神真可嘉老骨头Spock! 斯波克Do you have a moment? 有时间吗Of course, Nyota. 当然尼欧塔Y ou should have this back. 这个你该收回去It belonged to your mother. 这是你母亲的东西It is not in a V ulcan custom... 瓦肯人的习俗不允许...to receive again that thing which was given as a gift. 收回送出去的礼物Y ou guys break up? 你们分手了吗What did you do? 你做了什么A typically reductive inquiry Doctor. 怎么越问越低级医生Y ou know Spock, if an Earth girl says it's me not you. 斯波克如果一个地球女孩说怪她不怪你It's definitely you. 那绝对怪你Excuse me. 不好意思Commander Spock. Will you have a moment of yourtime?斯波克中校能耽误您一下吗Thank you for bringing me this into my attention. 谢谢你们告知我这个消息Live long and prosper. 生生不息繁荣昌盛Live long and prosper. 生生不息繁荣昌盛{\an8}{\fn方正黑体_GBK\fs18\b1\bord1\shad1\3c&H2F2F2F&}斯波克大使服役年限\N2230.06 - 2263.02{\an3\fs16\bord0\fn微软雅黑\fad(0,0)\b0\pos(374,247)}星际联邦大使进取号二副首席参谋I have an alert of incoming vessel. 警报有飞船靠近Unidentified non-federation. 非联邦飞船身份不明Attention, unidentified vessel. 未知飞船请注意Y ou are not authorized for approach. 你未被授权靠近本基地Power down and wait for instruction. 请关闭引擎原地等候指示Unidentified vessel, please comply. 未知飞船请遵从指示Just speak normally.请正常说话就好Language analysis complete. 语言分析完成{\an8}{\fn方正黑体_GBK\fs18\b1\bord1\shad1\3c&H2F2F2F&}宇宙通用翻译器We were on a science mission inside the nebula.我们在这个星云中执行科学任务Our ship suffered a critical malfunction.飞船发生了严重故障I took an escape pod. 在飞船坠毁在附近星球上前Before the ship crash landed on a nearby planet. 我用救生舱逃了出来We need a ship, capable of navigating the nebula. 我们需要一艘有能力穿梭这个星云的飞船Y ou must have someone, who can help us. 你们一定有人能帮助我们We tracked her stranded ship 我们穿过未标记的星云through the sector of uncharted nebula. 追踪到了她搁浅的飞船Here. 210, mark 14. 这里坐标210 标记14Long-range scan? 远程扫描呢No data. The nebula is too dense. It's uncharted space. 没有数据星云太稠密没人去过Well, the Enterprise does have 进取号确实有舰队中the best navigational systems in the fleet. 最出色的导航系统She can handle it. 她能完成这个任务The only ship here, with more advanced technology... 这里唯一技术更先进的星舰...is still under construction. 还在建造中But it's not just a ship that I am sending. 但我要派出去的可不只是一艘飞船I'll gather the crew. 我去召集船员Captain. 舰长Starfleet Command sent me 我从舰队指挥部your application for your vice-admiral position 收到了你的中将升职申请here at this installation.并且你想在这儿就职Y es, ma'am. 是的长官If I may, I would recommend Commander Spock... 如果可以我想推荐斯波克中校to replace me as a Captain of the Enteprise. 接任进取号的舰长一职He is an exemplary Starfleet officer. He'll make a great Captain. 他是星际舰队军官的典范他会是个好舰长It isn't uncommon, you know. 你的决定我并不意外Even for a captain, to want to leave. 即便是舰长也可能会想离开There's no relative direction in the vastness of space... 浩瀚的宇宙中没有相对的方向...there's only yourself. 只有你自己Y our ship, your crew. 你的飞船和你的船员It's easier than you think to get lost. 不知不觉就会迷失I'll bring it to talk with the General Council. 我会跟总理事会讨论你的申请We'll discuss it when you return. 等你回来我们再详谈- Mr. Spock. - Captain. -斯波克先生-舰长- I have something... - Perhaps there... -我有些事... -也许...- No, please. - Captain, after you. -没事你说吧-您先吧舰长I insist. 还是您先After this mission, we should... 这次任务后我们应该... ...we should sit down. There is something I need to talkabout.我有些事想跟你坐下来谈I, as well, have something to share. 我也有事想跟您说We make a good team, right? 我们配合得很好对吧I believe we do. 我相信是的I insist. 还是你先Lt. Uhura, open a ship wide channel. 乌胡拉上尉开启全舰通讯Y es, Captain. 是舰长Attention, crew of the Enterprise. 进取号全体船员请注意Our mission is straightforward. 我们的任务简单明了The rescue of a crew stranded on a planet in an uncharted space. 拯救一艘搁浅在未标记星域的飞船船员Our trajectory will take us through an unstable nebula... 导航路线将带我们穿越一片动荡的星云...one which will disable all communication withStarfleet.我们将与星际舰队失去一切联系We will be on our own. 我们将只能依靠自己The Enteprise has something no other ship in the fleethas.进取号有着舰队里其他星舰没有的Y ou. 就是你们As we've come to understand there's no such thing as the unknown. 多年来我们明白了没有未知的事物Only things temporarily hidden.只是尚未被发现Kirk out. 柯克讲话完毕Readings indicate cloud density diminishing, sir. 读数表明星云密度在降低长官This is Altamid. Our ship is stranded here. 这就是奥塔米德我们的飞船就搁浅在这Approaching Altamid. 靠近奥塔米德Class M planet. M级星球Massive subterranean development, 地表下大量建设发展痕迹but limited to no life forms on the surface... 但地表上没有任何生命形式存在Proximity alert, sir. 距离警报长官We have an unknown ship heading right for us. 有未知飞船朝我们过来了- Lt. Uhura, hail them. - Y es, Captain. -乌胡拉上尉呼叫他们-是舰长No response. 没有回应I'm picking up some kind of a signal.我接收到了某种信号They are jamming us. 他们在干扰我们Magnify, Mr. Sulu. 放大苏鲁先生What is this? 这是什么Shields up! Red alert! 升起防护盾红色警报Fire at will! 火力全开Sir, our phasers are having minimal effect 长官我们的相位炮威力太小and our torpedoes can't track the movement. 鱼雷也无法捕捉对方移动轨迹Fire everything we've got. 发射所有武器Captain, we are not equipped for this matter of engadgement. 舰长我们没有应对这种交火的装备Shields frequency has no effect, sir. 护盾频率没效果长官They took out the dish. 天线失灵了Shields are inoperable.护盾失效了- Warp us out of here, Mr. Sulu. - Y es, sir. -用曲速离开这里苏鲁-是长官Why the hell aren't we moving? 我们怎么没动I can not engage the warp drive, sir. 我无法启动曲速引擎长官Scotty, I need the warp now. 小科我现在就要曲速I can not, sir. 不行长官...they've gone. 它们被打掉了Security, engage all emergency procedures. 注意启用所有应急程序All personnel report to emergency stations. 所有人员到急救站报道I have hull breaches in levels 12 to 15, 船体的12至15层已有缺口6, 9, 31 and 21, sir. 还有6 9 31和21层长官Captain, in a 10 sec 舰长10秒后I could reroute the energy from the warp core 我可以从曲速核心抽取能量to the impulse engines. 接给脉冲引擎If we can get back into the nebula maybe we can lose them 如果能回到星云中也许能甩掉他们Do whatever you have to, Scotty. 该做什么就做吧小科Keenser let's go. 金瑟我们走All clear, Krall. 清理完毕克劳Connecting plasma pipes, stand by then you start it onmy mark!连接等离子管听我的命令启动I have the Abronath. Secure the ship. 我拿到阿博纳斯的碎片了封锁星舰- Captain. - Go, Spock. -舰长-说斯波克I've identified the individual who appears 攻击方由一个入侵者领导to be leading the attack party. 我已经确认了They infiltrated the archive vault, and removed theartifact他们从保险柜拿走了那个武器碎片from our mission on Teenax. 就是特纳科斯星的和平礼物Hold your distance until... 保持距离直到...Spock! Spock! 斯波克斯波克Y ou two, with me. Sulu, you have the conn. 你俩跟我来苏鲁你来指挥Y es, sir. 是长官My god! 我的天...the hell? 搞什么Doctor? 医生Doctor, we must evacuate now! 医生我们得马上撤离了Captain Kirk. 柯克舰长Y es! We have 100% impulse. 好了脉冲能量达到100%Great work, Mr. Scott! 干得漂亮斯科特先生Maximum impulse towards the nebula! 最大脉冲前往星云A y! 是{\an8\pos(193,226)}{\fn方正黑体_GBK\fs15\b1\bord0\shad1\3c&H2F2F2F&\fad(200,200)}克劳这艘飞船正想逃往星云{\an8\pos(237,207)}{\fn方正黑体_GBK\fs15\b1\bord0\shad1\3c&H2F2F2F&\fad(200,0)}切断她的喉咙Kirk to bridge. 柯克呼叫舰桥We are losing the inertial dampers. 我们正失去惯性阻尼器Systems are failing shipwide, Captain. 整艘飞船的系统都在崩溃舰长The emergency blockades are sealing... 紧急封锁正在尝试封闭损坏船体...but the structural integrity is at 18% and falling, sir. 但结构完整度只有18% 并且继续下降Abandon ship, Mr. Sulu. 弃船苏鲁先生Sound the alarm. 拉响警报We need to give those Pods a chance to escape 我们得给逃生舱增加逃脱成功的机会Can you lead the ship away? 你能把那些敌机引走吗The impulse engines are still 脉冲引擎还在尝试trying to draw power from the warp reserve. 从曲速存量中吸取能量We can not move until the saucer is separated. 只有等碟部分离了我们才走得了I'll handle it. 我来处理A ye aye, sir. 是长官We got to get you guys to escape pod. Go. 你们得去逃生舱快走Ensign Syl. 希尔少尉I need your help. 我需要你的帮助Y es, sir. 是长官My god! 我的天Spock, they are taking the crew. 斯波克他们在抓逃生舱里的船员Are you okay? 你还好吗saucer should be free by now. 碟部现在应该脱离了才对I know, Mr. Sulu. The Captain should be there. 我知道苏鲁先生舰长应该到了The impulse engines drawing power from auxiliarygenerators.脉冲引擎正从辅助发电机吸取能量Captain. 舰长How many of the crew is still in saucer? 碟部还有船员吗None. 没有了If I read this correctly... 如果我没看错...the intruders are taking them. 入侵者在抓捕他们Captain, we're caught in the planet's gravity. 舰长我们已进入了这个星球的重力范围We can not pull away. 已经没有足够动力离开Get your Kelvin pods. 快进开尔文逃生舱- Y es, sir. - A y, Captain. -是长官-是舰长Come on! Let's go! 走吧我们走Y ou knew... 你早就知道Y ou knew we would be attacked. 你知道我们会被袭击Y ou don't understand. 你不明白Captain Kirk. 柯克船长Y es, I lied. 对我骗了你们Our ship was attacked. 我们的飞船被袭击了Chekov, check the comms for survivors. 切科夫检查通讯器扫描幸存者A ye aye, aye Captain. 明白舰长- Who is he? - His name is Krall.-他是谁-他叫克劳He took my crew, like he took yours. 他抓了我的船员就像抓你们的船员一样How did he know so much about the Enterprise? 他怎么会对进取号这么了解All I know is that if I did this... 我只知道如果我引你们前来...he'll set them free. 他就会放了我的船员Chekov, are you picking anything upon those scanners? 切科夫扫描仪上有接收到什么吗Nothing Sir. 什么都没有- What if they... - No, no. -会不会他们都... -不不可能He was taking them. 他们只是被抓了We have to find that saucer even 我们得找到碟部minimal scanning systems will have more range than tricorders. 即使最小的扫描系统也比三录仪扫距更长A ye, Captain. It's possible. 是的舰长有可能Captain, I was protecting my crew. 舰长我只是在保护我的船员What is your name? 你的名字是什么How do you know our language? 你怎么会我们的语言I know your kind. 我了解你们人类I'm Lt. Nyota Uhura of the U.S.S. Enterprise. 我是尼欧塔·乌胡拉上尉联邦星舰进取号And you have committed an act of war against Fede... 你的行为已被视作对星际联邦宣战Federation. 星际联邦Federation is an act of war. 星际联邦的存在就是战争行为Y ou attacked us. 是你袭击了我们Y our captain... 你们的舰长Why did you sacrifice yourself for him? 你为什么为了他牺牲自己He would have done the same. 他也会做同样的事And if he made it off that ship, he will come for us. 他若从舰上幸存一定会来救我们I'm counting on it, Lt. Uhura. 正如我所愿乌胡拉上尉I can't believe it. 简直难以置信My god, Spock! 天哪斯波克Sit down over here. 快来这里坐下Okay, easy, easy. 好了小心小心Okay. I'll just a... 好了我来Try to relax. Y ou're going to be okay. 试着放松你会没事的Forced optimism in your voice suggests 你语气中强行乐观的成分表明you are trying to enlist a sense of calm in order to ... 你试图挤出点镇定来安抚...Cut the horse shit. 少扯狗屁Doctor, I failed to see how excrement of any kind bearsrelevance医生我不明白动物的屁股与我们in our current situation. 现在的情况有任何关联- What the hell are you doing? - We must keep moving, doctor. -你要干什么-医生我们得继续走Spock, this thing punched your iliac region. 斯波克这东西刺穿了你的腹股沟Time is a critical factor. 得抓紧时间That's exactly what I am trying to tell you. 我也是说要抓紧时间赶快走啊Look, if I can't take this out, you're gonna die. 听着我要是不取出来你会死Okay, if I take it out and 如果我取出来can't stop the bleeding, you are gonna die. 但止不了血你也会死I can't see no appealing in neither option. 两个选择都不咋地Believe me or not, neither can I. 没错我也是这么想So, if I remember correctly 如果我没记错的话The V ulcans have your hearts where humans have their livers. 你们瓦肯人的心脏在人类的肝脏部位That is correct, doctor. 没错医生That explains a thing or two. 难怪你这样了Y ou know, you are lucky. A inch to the left... 你知道你很幸运如果再往左三厘米...and you would be dead already. 你就已经死了I just don't get it, Spock. 我就是不明白斯波克What did they attack us for? I mean... 他们为什么要攻击我们They do all this for some 难道就为了个小矮子们doodad with the tiny Clevers didn't want? 都不想要的小玩意儿It is unwise to trivialise that 仅仅因为不理解which one simply does not understand, Doctor. 就认为其微不足道是不明智的行为医生We can safely assume that it's more important than adoodad.反正肯定不止是个小玩意了I think you just managed to insult me twice, Spock. 你成功侮辱了我两次斯波克Alright, Spock. 好吧斯波克Just got one question. 我只有一个问题- What's your favorite color? - I fail to see the relevance... -你最喜欢什么颜色-我看不出来...Y eah, they say it hurts less if it's a surprise. 他们说毫无准备时痛感最小看来没错I may have a doctor parlance with which you arefamiliar...用你熟悉的医学术语来说...I can confirm your theory to be horse shit. 你这话简直是狗屁We've got to get out of here. 得闪了Y ou're kidding me, aren't you? 你开玩笑吧Hello there. 各位好My name is Montgomery Scott... and... 我叫蒙哥马利·斯科特...who might you be? 你们是谁Watch it, sonny. I am pretty handy when I want to be... right. 当心点小伙子必要时我可是很能打的Don't come back. 千万别回来Well, we certainly show them uh lassie 我们可给了他们些颜色瞧瞧小姑娘Hey! That's Starfleet property, Okay. 喂那是星际舰队的财产Y ou can not just take them and.... 你不能随便拿......but, I'm feeling generous today so how about it. 好吧我今天很慷慨所以随便拿吧Where did you get that? 这个是从哪里来的- Is that English? - I learned it from my house. -你说英文-我从我的房子里学的Where did you get that ? 这个是从哪里来的- This is my Starfleet insignia. - What does it mean ? -这是我的星际舰队徽章-这是什么意思Means that I am an officer of Starfleet. Engineeringdivision.证明我是星际舰队工程部的一员- Engineering? - A ye, that's right, I fix things. -工程部-对修修东西什么的I know what is engineering. 我知道工程部是什么Y ou're not with those bastards that killed my ship, are ya? 你和那些毁了我飞船的人不是一伙的对吧I take that as a no. 我就当不是了He is Krall. Him and his... 他是克劳他和他的...bees. 蜜蜂们They search the stars for a death machine. 他们在星际间寻找一个死亡武器这也是包括你我所有人在这的原因They are the reason why you are here, why we are allhere.Even those 3 scunners? 也包括那三个讨厌鬼They have fallen from the sky, like me and you. 他们也是坠毁飞船的幸存者跟你我一样Come with me. Now! 跟我走现在等等小姑娘我今天过得很不顺Wait, hang on a minute, lassie. I'm having a difficult dayhere.I gotta find my crew mates. 我得找到我的同伴I will help you find your mates... 我会帮你找到同伴...and then you will help me. 然后你也要帮我With what? 帮你干什么- Y ou want me to fix something? - Y es. -你想让我修东西-对Y ou help me and I help you. 你帮我我帮你Alright, well things being as they are 好吧既然事情已经这样了I doubt I'll get a better offer today. 恐怕我也没有更好的选择So lead the way. 带路吧Good. 很好I am Jaylah. 我叫婕拉- And you're Montgomery Scott. - A ye, Scotty. -你是蒙哥马利·斯科特-叫我小科Come now, Montgomery Scotty. 跟我走蒙哥马利·小科Alright, hold up. 好吧等我The Enterprise. 进取号She may not even have power to the bridge, Captain. 她可能都无法给舰桥供电了舰长She still has a few tricks up her sleeve. 她还没完全瘫痪呢I bet on it. 我敢打赌McCoy to Enterprise, come in. 麦考伊呼叫进取号请回答McCoy to Enterprise. 麦考伊呼叫进取号Hey, take it easy there, Spock. 慢点儿斯波克That was just a temporary fix back there. 刚才只是应急处理I understand, Doctor. 我明白医生Fascinating. 有趣Omuns, dark, dangerous. 不详黑暗危险We are going in. 反正要进去Intriguing. 有趣These symbols are the same images as those 这些符号和他们想抢走的depicted on the artifact taken in the attack. 那件武器上的图案一模一样Y ou think it came from here? 所以武器原本就来自这里It would seem so. 看样子是的Damm it... Spock! 该死斯波克Easy.Easy. 放松放松Hurry. 快- Aren't we there yet? - Stop asking that. -到了吗-别再问了- Sorry. - This is the way, come. -对不起-走这条路Watch your steps, you do not want to set off my traps. 小心脚下可不要踩到我的陷阱上Oh, that's clever. 真聪明What is this place? 这是什么地方- This is my house. - Y our house? -这是我的房子-你的房子Hold on a minute. 等等Is this a ship? 这是一艘飞船I hope you find your friends and you help me fix it. 我希望你找到你的伙伴然后帮我修好它So I can leave this planet forever. 我就能永远离开这个星球了Wo... Wait a minute. 等等Is this your ship? 这是你的飞船No, Montgomery Scotty. 不蒙哥马利·小科It's yours. 这是你们的飞船Oh my good lord. 我的天啊{\an8}{\fn方正黑体_GBK\fs18\b1\bord1\shad1\3c&H2F2F2F&}联邦星舰富兰克林号星舰编号NX-326{\an3\fs16\bord0\fn微软雅黑\fad(0,0)\b0\pos(374,247)}Frank Lin是导演父亲名字老版斯波克演员伦纳德·尼莫伊生日是3月26日Captain, it looks like there is power. 舰长看起来能量应该还有剩Alright, let's get to the bridge and find the crew. 好我们去舰桥用飞船上的扫描仪找其他人The console is intact, and I will... 控制台还完整我可以...try to reroute power to it. 试着重接电源Work fast. 动作快点Once we get this place lite up, we are gonna draw a lot ofattention.我们这里一亮会引起不少注意What do you think? Can you find them? 能找到他们吗A ye, Captain. 可以舰长I am reconfiguring scanners to modulate for the crews sequence. 我正在重设扫描频率为船员通讯频率Y ou with me. I left something behind.你跟我来我留了点东西在飞船上That is one heck of a cold. 你这是什么感冒啊Nice job, Keenser. 干得好金瑟Alright, we've got about 15 minutes until the next guard rotation. 好了离下一班士兵巡逻还有15分钟Come on. 快来Let's go. Come on. 快走Come on! 走This is a Magellan probe. 这是麦哲伦探测仪联邦就是靠这个在星云中导航的Federation was using these to find a way through thenebula.What's he using it for? 他用来干什么What do you see? 你看出什么了他在探测仪间继承了子空间链接He's been piggybacking the subspace links between theprobes.Can we use it to send a distress signal? 那可以用这个发送求救信号吗I can try. 我试试{\an8}{\fn方正黑体_GBK\fs18\b1\bord1\shad1\3c&H2F2F2F&}访问中Sent. 已发He's accessed the Y orktown database. 他潜入了约克镇联邦基地的数据库What? 什么He's got Startfleet data files... ship logs... 这是星际舰队的数据资料航行日志...including the Enterprise. 包括进取号的He's been watching us this whole time. 所以他一直在监视我们Captain... 舰长...the artifact was on the ship the whole time? 那件武器其实一直在舰上I cannot afford to get caught with it. 我不能冒险带着这东西被抓So I hid it in here. 所以我藏在了船上Tell Krall... I have the Abronath. 告诉克劳我拿到阿博纳斯了Do you believe every sad story you hear? 你听到悲惨故事就信吗Not every. 你这个我就没信Put the phaser down. Please. 请把枪放下Did you get it, Chekov? 你追踪到了吗切科夫A ye, Captain. I've traced her location of her comm. 是的舰长我追溯到了通信对象的位置What does Krall want with this thing? 克劳要这个有什么用To save you. 从你们自己手上From yourselves. 拯救你们Captain! 舰长- Y ou all right? - A ye, Captain, but we are trapped. -你还好吗-我们被困住了Can you get this thing started? 你能启动这个吗Have you intermitted the intuition…engage the你是不是疯了启动推进器thrusters?I am open up to other suggestions. 有更好的建议就请讲Okay. 好吧- There's the problem, sir. - What? -有个问题长官-什么问题Fuel is pumped. I cannot get into combust. 燃料已传送到推进器但我不能点。
超能末世者第三集250字作文英文回答:In the grim world of "Supernatural Apocalypse", the third episode unfolds with startling intensity. As the survivors band together to decipher the origins of the cataclysm, new threats emerge, testing their resilience to the limits. The episode's pacing is relentless, constantly shifting between heart-stopping action sequences and moments of quiet introspection.At the heart of the episode is the enigmatic figure of Anya, a young woman who possesses extraordinary powers. Her journey of self-discovery becomes a catalyst for the survivors to question their own limits and the nature of the supernatural forces that have consumed their world. The episode delves into themes of identity, acceptance, and the indomitable will to survive.The production values are top-notch, with stunningspecial effects and a cast that delivers compelling performances. The cinematography is evocative, capturing the desolate landscapes and the desperate struggles of the characters. The sound design is equally impressive, immersing the viewer in the chaos and peril of the supernatural apocalypse.Overall, the third episode of "Supernatural Apocalypse" is a thrilling and thought-provoking chapter that sets the stage for an epic season. It's a must-watch for fans of the genre and anyone seeking an immersive and captivating storytelling experience.中文回答:在《超能末世者》的第三集中,故事以惊人的强度展开。
Lesson3 An unknown goddess无名女神课文Some time ago,an interesting discovery was made by archaeologists on the Aegean is land of Kea.An American team explored a temple which stands in an ancient city on t he promontory of Ayia Irini.The city at one time must have been prosperous,for it en joyed a high level of civilization.Houses -- often three storeys high -- were built of st one.They had large rooms with beautifully decorated walls.The city was even equipped with a drainage system,for a great many clay pipes were found beneath the narrow streets.The temple which the archaeologists explored was used as a place of worship from the fifteenth century B.C.until Roman times.In the most sacred room of the temple,clay fragments of fifteen statues were found.Each of these represented a godd ess and had,at one time,been painted.The body of one statue was found among rema ins dating from the fifteenth century B.C.Its missing head happened to be among rem ains of the fifth century B.C.This head must have been found in classical times and ca refully preserved.It was very old and precious even then.When the archaeologists rec onstructed the fragments,they were amazed to find that the goddess turned out to be a very modern-looking woman.She stood three feet high and her hands rested on her hi ps.She was wearing a full-length skirt which swept the ground.Despite her great age, she was very graceful indeed,but,so far,the archaeologists have been unable to disc over her identity.译文不久之前,在爱琴海的基亚岛上,考古工作者有一项有趣的发现。
Words and expressions核心单词默写Unit 1laugh out loud1 ________________ n.心情2 ________________ n.马戏团3 ________________ n.娱乐,消遣4 ________________ 游乐场5 ________________ adj.卷曲的6 ________________ n.假发7 ________________ n.徽章8 ________________ n.脚踝9 ________________ n.小丑10 ________________ v.使快乐11 ________________医疗保健12________(使)高兴起来,(使)振作13________________奏效,达到预期效果14 ________________ v.检查(身体)15 ________________ n.广告16 ________________ n.雇用者,雇主 17_____________adj.极其重要的,必不可少的18 _____________v.使钦佩,使留下深刻印象19 ________________ v.露齿而笑,咧着嘴笑20 ________________ v.应得,应受到21 ________________愁眉苦脸 22 ________________笑料,笑柄23 ________________笑了起来24 ________________ 恶作剧25 ________________ n.名声,声誉26 ________________ n.语言学家 27 ____________adj.说话风趣的;妙趣横生的28 ______________adj.中世纪的,中古时期的 29 ________________ 使情绪激动的30 ________________ adj. 调皮的,淘气的 31 ________________ n.言论,意见,评论32 ________________ n.交流33 ________________ n.男理发师 34 ________________ n.刮脸,刮胡子35 ________________ n.男人,家伙36 ________________ n.品牌,牌子37 ________________某种类型的幽默38 ________________ n.概念;观念39 ________________ n.地点,处所40 ______________(故意提出难以回答或尴尬的问题)使某人难堪41 ________________ adj.残忍的42 _______________ v.哄笑,大笑43 ________________ adv. 温和地;轻柔地44 ________________斥责,责骂45 ________________ v.照亮,照明46 ________________ n.等式,方程47 ________________ adj.难处理的;难懂的48 ________________ v.结束,终止49 ________________ n.作曲家50 ________________不能按时完成(工作)外研版(2019)选择性必修第一册Unit 2 Onwards and upwards1 _______________ /det/ n. 债务,欠款2 _____________ n.速度,进度3 _____________ v.通知,告知4 _____________ v.畏惧,惧怕5 _____________ adv.很少,难得6 _____________adv.突然,一下子7 _____________ n.拒绝,否决8 _____________ / adv.然而,不过9 _____________ v.锲而不舍,坚持不懈10 ____________n.批评,职责11 _____________ n.手稿,底稿12 _____________ adj.令人愉快的,讨人喜欢的13 _____________/ n.畅销书,畅销产品14 _____________adj.文学的15 _____________ adj.难堪的,尴尬的16_____________ adj.长久的;永久的17 _____________ n.名著,经典作品18 _____________n.(忍)耐力19 _____________ v.保证,确保20 _____________ adj.愉快的,高兴的 21 _____________n.结果,后果22 _____________adj.重要的,值得做的23 _____________ n.香味24 _____________n.享受,乐趣25 _____________ adj.强有力的,雄伟的26 _____________ adj.热心的,热衷的27_____________ n.比赛,竞赛28 ___________adj.心烦意乱的,烦恼的29 _____________v.选举,推选30 _____________ n.幸事,幸运31 ____________ adj.感激的32 _____________ adj.值得尊敬的;值得赞赏的33 _____________of 值得……的34 _____________ 触觉的35 _____________ n.和蔼,温和36 _____________n.友谊,友好交往37 _____________ n.指尖38 _____________ n.外形,轮廓39 _____________ v. 使兴奋,使陶醉40 _____________n.(某人)常去的地方41 the_____________ of (历史事件的)缤纷场景42 _____________ v.调查,探究43 _____________ v.降临;来临44 _____________ n.使人高兴的事45 _____________ n.展现,显示46 _____________ adj.平凡的,平淡的47 _____________ prep. 在……之中外研版(2019)选择性必修第一册Unit 3 faster, higher , stronger Words and1 __________________from与……大不相同2_____ adj.光滑发亮的,闪光的3 __________ n.协会,社团4 ________ adj.沾满泥的,泥泞的5 ______________n.投球,射球,击球6 _________________ n.篮板7 _________________倒塌,向下垮8 _________________ n.隆起之处9 _______v.(使)弹起,(使)反弹10 __________ v.使提高,使改进11 _________________ n.队友12 __________ n.脚步声,足迹13 _________________ 仿效某人;继承某人(尤指家人)的事业14 _________________ 继续15 ______________ n.武士,战士16 ___________ / n.预料,预期17 _________________超出某人的预期18 _________________ 连续地19 _________________n.人生哲学20 _________________ n.自信21 ___________n.锦标赛22 _________________v.欺骗,作弊23 ____________ n.合作,协作24 _________________ 滑旱冰25________adj.非凡的;不寻常的26 _________________ /net/ n.网球27 _________________ n.(排球队的)扣球队员,主攻手28 _________________ v.突然出现29 _________________ 突然出现在……(指突然成功)30 __________ adj.生动的,逼真的31 _________________v.分配,分派32 _________________ n.(竞争、比赛等的)对手33_____________ .合作,协作34 _________________ adj.初步的;预备的35 __________ adj.紧张的,激烈的36 _________________取得成功37 ____________ n.东山再起38 _________________ v.战胜,打败39 _________________ n.(完成某事的)要素,因素 40 __________ adj.钢铁般的;坚定的41 _________________ n.意志力42 _________________ /si:z/ 夺取外研版(2019)选择性必修第一册Unit 4 Meeting the Muse1 _______________ n. 引文,引语2 ___________ adv.根据字面意思3 _______________ v.漂,浮4 _______________ adj.民间的,民俗的5 _______________ n.故事6 _______________民间故事7 _______________ / n.动,运动8 _______________ 使……开始运动9 _______________/ v.作(曲)10 _______________ v.蹲下,蹲伏11 ______________ n.动画片12 _______________n.公主13 _______________ adj.民族的14 ______________adj.抽象(派)的15 _______________ adj.令人起敬的,令人钦佩的16 _______________ n.现代雕塑装置(除物体外嗨包括光、声等)17_______________n.革新,创新18 ______________n.电缆19 _______________ adj.新颖的,创新的20 _______________n.趋势,动向21_______________ n.巧匠22 _______________ n.反差,对比23 _______________ adj.清晰的;明显不同的外研版(2019)选择性必修第一册Unit 5 revealing natureWords and expressions核心单词默写1 ______________________n. 种子,籽2 ___________________ adj.遥远的3 ___________________响应号召4 ___________________ n.丢脸,耻辱5 _________________ 是耻辱,是丢脸的事6 ____________ n.地质学家7 ___________________ n.样本8 ___________________v.进化9 ________________ n.厘米10 _______________v.把……联系起来;连接11 ______________v.猜想,怀疑,觉得12 ______________ n.(动物的)原种,祖先13 __________________n.进化(论)14 __________________v.产生,创造15 ___________________ n.特征,特性16 ___________________ v.减少17 ___________________ n.网络犯罪18 ___________________v.责怪,指责;把……归咎于19 ___________________n.(古代的)神话20 ______________源于……的,原产于……21 _________________ adj.原始的,低等的22 __________________ adv.遍及全世界23 ___________________ / adj.巨大的,特大的24 _________________d/ n.传说,传奇(故事)25 ___________________v.发现,察觉(尤指不易觉察到的事物)26 __________________ n.杀虫剂,农药。
a r X i v :a s t r o -p h /0110633v 1 29 O c t 2001Mon.Not.R.Astron.Soc.000,1–11(2001)Printed 1February 2008(MN L A T E X style file v1.4)Evolution of a 3M ⊙star from the main sequence to the ZZCeti stage:the role played by element diffusionL.G.Althaus ⋆,A.M.Serenelli †,A.H.C´o rsico ‡and O.G.Benvenuto §Facultad de Ciencias Astron´o micas y Geof´ısicas,Universidad Nacional de La Plata,Paseo del Bosque S/N,(1900)La Plata,Argentina E-mail:althaus,serenell,acorsico,obenvenu@.ar1February 2008ABSTRACTThe purpose of this paper is to present new full evolutionary calculations for DA white dwarf stars with the major aim of providing a physically sound reference frame for exploring the pulsation properties of the resulting models in future com-munications.Here,white dwarf evolution is followed in a self-consistent way with the predictions of time dependent element diffusion and nuclear burning.In addition,full account is taken of the evolutionary stages prior to the white dwarf formation.In par-ticular,we follow the evolution of a 3M ⊙model from the zero-age main sequence (the adopted metallicity is Z=0.02)all the way from the stages of hydrogen and helium burning in the core up to the thermally pulsing phase.After experiencing 11thermal pulses,the model is forced to evolve towards its white dwarf configuration by invoking strong mass loss episodes.Further evolution is followed down to the domain of the ZZ Ceti stars on the white dwarf cooling branch.Emphasis is placed on the evolution of the chemical abundance distribution due to diffusion processes and the role played by hydrogen burning during the white dwarf evolution.We find that discontinuities in the abundance distribution at the start of the cooling branch are considerably smoothed out by diffusion processes by the time the ZZ Ceti domain is reached.Nuclear burning during the white dwarf stage does not represent a major source of energy,as expected for a progenitor star of initially high metallicity.We also find that thermal diffusion lessens even further the importance of nuclear burning.Furthermore,the implications of our evolutionary models for the main quantities relevant for adiabatic pulsation analysis are discussed.Interestingly,the shape of the Ledoux term is markedly smoother as compared with previous detailed studies of white dwarfs.This is translated into a different behaviour of the Brunt-V¨a is¨a l¨a frequency.Key words:stars:evolution -stars:interiors -stars:white dwarfs -stars:oscillations1INTRODUCTIONOver the last few years,radial and particularly non-radialstellar pulsations have become a very powerful tool for in-quiring into the internal structure and evolution of stars.Thanks to the increasing degree of sophistication both in⋆Member of the Carrera del Investigador Cient ´ıfico y Tec-nol´o gico,Consejo Nacional de Investigaciones Cient ´ıficas y T´e cnicas (CONICET),Argentina.†Fellow of CONICET,Argentina.‡Fellow of CONICET,Argentina.§Member of the Carrera del Investigador Cient ´ıfico,Comisi´o n de Investigaciones Cient ´ıficas de la Provincia de Buenos Aires,Argentina.theoretical and observational techniques,asteroseismologyhas been successfully applied to decipher the oscillatory pat-tern of numerous pulsating stars,amongst them our Sun represents the best example.With the advancement and re-finement of observations,a large number of stellar objects located in a variety of places in the Hertzsprung-Russell dia-gram has gradually manifested themselves in non-radial pul-sators.Indeed,variable stars covering several evolutionary stages,such as roAp,SPB,δScuti,βCephei and variable white dwarfs have been classified as non-radial pulsators (see,e.g.,Cox 1980;Unno et al.1989;Brown &Gilliland 1994and Gaustchy &Saio 1995,1996).To this class belong also the recently discovered sdB (Kilkenny et al.1997)and γDoradus (Kaye et al.1999)variable stars.From the observational point of view (with the ob-c2001RAS2L.G.Althaus,A.M.Serenelli,A.H.C´o rsico and O.G.Benvenutovious exception of our Sun),white dwarfs represent one of the best established and extensively studied kind of non-radial pulsators.Pulsating white dwarfs exhibits multi-periodic luminosity variations in three different regions of the Hertzsprung-Russell diagram corresponding to the cur-rently called DOV(and PNNV),DBV and DAV(see,e.g., the review by Winget1988).Of particular interest in this work are the DAVs(hydrogen-rich atmospheres),or ZZ Ceti stars,that are found to pulsate in the instability strip corre-sponding to the effective temperature(T eff)range of12500 K≥T eff≥10700K.The periodicities in their light curves are basically explained in terms of non-radial g-modes of low harmonic degree(ℓ≤2),driven by theκ−γmecha-nism working in a partial ionization region below the stellar surface(Dolez&Vauclair1981;Winget et al.1982)¶.The periods are found within a range of100-1200s and photo-metric amplitudes reach up to0.30magnitudes.Numerous studies have been devoted to analysing the pulsation char-acteristics of DAV white dwarfs.Amongst them,we mention the works by Tassoul,Fontaine&Winget(1990),Brassard et al.(1991,1992ab),Bradley&Winget(1994),Gautschy, Ludwig&Freytag(1996)and Bradley(1996,1998,2001).In order to fully understand the oscillatory properties of DAV white dwarfs and to take full advantage of the rich-ness offered by available observations,physically sound stel-lar models are required.In the context of these pulsating stars,most of the existing research rests on stellar models constructed under the assumptions of some simplifying hy-pothesis.This is particularly true with regard to the treat-ment of the chemical abundance distribution.In this sense, carbon and oxygen profiles are usually treated as free pa-rameters.In addition,the chemical abundance distribution is assumed to befixed during the evolution across the in-stability domain and in some cases the diffusive equilibrium approximation is invoked to assess the shape of the chemical profile at the interface regions.Hydrogen burning is likewise neglected in the construction of evolutionary models em-ployed in pulsation studies of ZZ Ceti stars.The neglect of hydrogen burning is only justified if the white dwarf is formed with relatively thin hydrogen layers.However,if the hydrogen envelope is massive enough,hydrogen burning re-actions constitute an appreciable source of energy even dur-ing the evolutionary stages corresponding to the ZZ Ceti domain(Iben&Tutukov1984).The details of burning are more complex if element diffusion is allowed to operate.In-deed,white dwarf evolutionary calculations in which time dependent element diffusion is properly accounted for(Iben &MacDonald1986)show that nuclear burning via the CN reactions plays a different role depending on the mass of the helium buffer region between the hydrogen-rich envelope and the carbon-and helium-rich underlying layers.For instance, a diffusion-induced hydrogen shellflash is expected to occur if the helium buffer is sufficiently less massive.How massive the helium buffer can be depends critically on the phase in the helium shellflash cycle during the thermally pulsing stage at which the progenitor departs from the asymptotic ¶However,Brickhill(1991)proposed the convective driving mechanism as being responsible for the overstability of g-modes in DAVs(see also Goldreich&Wu1999).giant branch(AGB)(see D’Antona&Mazzitelli1990for details).Obviously,the construction of stellar models of DAV white dwarfs appropriate for pulsation studies in which the above mentioned issues are fully taken into account requires evolutionary calculations considering not only time depen-dent element diffusion but also a detailed treatment of the evolutionary stages prior to the white dwarf formation.The calculation of such stellar models is the main purpose of the present work and to the best of our knowledge such an en-deavour has never been attempted.The primary application of the DA white dwarf evolutionary models to be presented here will be the exploration of their pulsation properties in future papers.Specifically,in this paper we shall limit our-selves to discuss the evolutionary results and their implica-tions for the main quantities entering the adiabatic pulsation equations.White dwarf evolution treated in a self-consistent way with time dependent element diffusion is an important as-pect of the present work.In most of previous pulsation stud-ies,the equilibrium diffusion in the trace element approxi-mation has been used to specify the shape of the chemical profile at the composition transition region of evolving stel-lar models(see Tassoul et al.1990;Brassard et al.1991, 1992ab;Bradley1996,1998,2001;Bradley&Winget1994; Montgomery,Metcalfe&Winget2001).However,the equi-librium approach for diffusion is not valid when diffusion time scales are comparable to the evolutionary ones.In par-ticular,diffusive equilibrium in the deep layers of the white dwarf model is not an adequate approximation even at the ages characteristic of the ZZ Ceti stage.In fact,it is found that during such stages,diffusion modifies the spatial dis-tribution of the elements,particularly at the chemical inter-faces(see Iben&MacDonald1985).For a proper treatment of the diffusively evolving stratifications,we consider in this work the processes of gravitational settling,chemical and thermal diffusion following the treatment of Burgers(1969) for multicomponent gases.In the context of DA white dwarf evolution,the treatment for diffusion we shall use here has been employed by Iben&MacDonald(1985,1986).In ad-dition,Dehner&Kawaler(1995)have used non-equilibrium diffusion star models for studying the connection between DO and DB white dwarfs.The shape of the composition transition zone is a matter of the utmost importance as far as asteroseismology is concerned.In particular,it contributes to the shape of the Ledoux term appearing in the Brunt-V¨a is¨a l¨a frequency(Brassard et al.1991)and plays a critical role in the phenomenon of mode trapping in white dwarfs (see Tassoul et al.1990;Brassard et al.1992a and references cited therein).Another important aspect of the present study is that the evolutionary stages prior to the white dwarf formation are fully taken into account.Specifically,we started our cal-culations from a3M⊙stellar model at the zero-age main sequence(ZAMS)and we follow its further evolution all the way from the stage of hydrogen and helium burning in the core up to the tip of the AGB where helium ther-mal pulses occur.To assure a full relaxation of the helium zone(see Mazzitelli&D’Antona1986),we computed a rea-sonable number of thermal pulses,after which the progeni-tor is forced to evolve towards its white dwarf configuration by invoking strong mass loss episodes.We shall concentratec 2001RAS,MNRAS000,1–11Evolution of a3M⊙star from the main sequence to the ZZ Ceti stage3on the particular situation that the white dwarf progenitor departs from the AGB when stationary helium burning pri-marily supports the star luminosity,following the occurrence of the last helium thermal pulse.We have not invoked addi-tional mass losses during the planetary nebula stage or early during the cooling branch.This will allow us to examine the maximum mass value for the remaining hydrogen content as predicted by the particular case of evolution analysed in this work,enabling us to explore the role played by nuclear burning during the cooling stages.The paper is organised as follows.In Section2we de-scribe our evolutionary code and the treatment we follow for element diffusion.In Section3we present in detail the evolutionary results for the white dwarf progenitor,giving particular emphasis to the thermal micro-pulses appearing towards the end of core helium burning and the thermally pulsing phase during thefinal AGB evolution.In this sec-tion,we also present the results for the post-AGB and white dwarf evolution.Attention is focused mainly on the evo-lution of the chemical distribution resulting from diffusion processes and the role of nuclear burning during the white dwarf regime.The implications of the evolutionary results for the main quantities relevant for adiabatic pulsation anal-ysis are detailed in Section4.Finally,Section5is devoted to summarizing our results.2COMPUTATIONAL DETAILSThe calculations presented in this work have been performed with the stellar evolutionary code developed at La Plata Observatory.The code has been used in our previous stud-ies on white dwarf evolution(Althaus&Benvenuto1997, 2000;Benvenuto&Althaus1998),and it has recently been appropriately modified in order to calculate the evolution-ary stages prior to the formation of white dwarfs.In broad outline,the code is based on the method of Kippenhahn, Weigert&Hofmeister(1967)for calculating stellar evolu-tion.In particular,to specify the outer boundary conditions we carried out three envelope integrations from photospheric starting values inward to afitting outer mass fraction,which is located in mass near the photosphere.The interior solu-tion is obtained via the canonical Henyey iteration scheme as described by Kippenhahn et al.(1967).To improve the numerical stability of our code,the Henyey scheme is ap-plied to the differences in the physical quantities(luminos-ity,pressure,radius and temperature)between the previous and the computed models.In addition,models were divided into approximately1500mesh points and time steps were maintained small enough so as to get a reasonable numer-ical accuracy during the thermal pulses at the tip of the AGB.Mesh distribution is regularly updated everyfive time steps.Our algorithm inserts mesh points where they are most needed,that is where physical variables change appre-ciably,and eliminates them where they are not neccesary. We want to mention that the entire evolutionary sequence from the ZAMS to the white dwarf stage comprises about 60000stellar models.The constitutive physics are as detailed and updated as possible.Briefly,it comprises OPAL radiative opacities (including carbon-and oxygen-rich opacities)for arbitrary metallicities(Iglesias&Rogers1996),complemented at low temperatures with the molecular opacities from Alexander& Ferguson(1994).In particular,opacities for varying metal-licities are required during the white dwarf regime whenaccount is taken in the calculations of element diffusion. Conductive opacity for the high-density regime is from Itohet al.(1983)and Hubbard&Lampe(1969)for low den-sities.Neutrino emission rates for pair,photo,plasma and Bremsstrahlung processes have been taken into account ac-cording to the formulation of Itoh and collaborators(seeAlthaus&Benvenuto1997for details).As far as the equa-tion of state is concerned,we have included partial ioniza-tion,radiation pressure,ionic contributions,partially de-generate electrons and Coulomb interactions.For the white dwarf regime,we employ an updated version of the equa-tion of state of Magni&Mazzitelli(1979).We have consid-ered a network of30thermonuclear reaction rates for hy-drogen burning(corresponding to the proton-proton chainand the CNO bi-cycle)and helium burning.Nuclear reac-tion rates are taken from Caughlan&Fowler(1988)except for the reaction12C(α,γ)16O which is taken from Anguloet al.(1999)(this rate is about twice as large as that ofCaughlan&Fowler1988).Electron screening is from Gra-boske et al.(1973)and Wallace,Woosley&Weaver(1982).The change in the chemical composition resulting from nu-clear burning is computed by means of a standard implicit method of integration.In particular,we follow the evolu-tion of the chemical species1H,3He,4He,7Li,7Be,12C, 13C,14N,15N,16O,17O,18O and19F.Convection has been treated following the standard mixing length theory(B¨o hm-Vitense1958)with mixing-length to pressure scale heightα=1.5.The Schwarzschild criterium was used to deter-mine the boundaries of convective regions.Overshooting andsemi-convection were not considered.In this work,we follow the evolution of an initially3 M⊙star starting at the ZAMS.The adopted metallicity Z is Z=0.02and the initial abundance by mass of hydrogen and helium are,respectively,X H=0.705and X He=0.275(rep-resentative for solar values as given by Anders&Grevesse 1989).Evolution has been computed at constant stellar mass all the way from the stages of hydrogen and helium burning in the core up to the tip of the AGB where helium thermal pulses occur.To achieve a white dwarf configuration,an ar-tificial mass loss has been incorporated in our evolutionary code.Specifically,mass loss was initiated when the white dwarf progenitor was about to experience its eleventh ther-mal pulse.The adopted mass loss rate was10−4M⊙yr−1 and it was applied to each stellar model as evolution pro-ceeded.After the convergence of each new stellar model, the total stellar mass is reduced according to the time step used for the model and the mesh points are appropriately adjusted.We want to mention that because of the high com-putational demands involved in the calculation we perform here,particularly regarding the treatment of white dwarf evolution with diffusively evolving abundances(see below), we shall restrict ourselves exclusively to examine one case of evolution for the white dwarf progenitor,deferring a more detailed exploration of different possibilities of white dwarf formation to future works.The evolution of the chemical abundance distributiondue to diffusion processes during the whole white dwarf stage represents an important aspect of the present study.In our treatment of element diffusion we have considered gravita-c 2001RAS,MNRAS000,1–114L.G.Althaus,A.M.Serenelli,A.H.C´o rsico and O.G.Benvenutotional settling,and chemical and thermal diffusion of nuclear species.To this end,we adopted the treatment for multi-component gases presented by Burgers(1969),avoiding the use of the trace element approximation usually assumed in white dwarf studies.It is worth noting that when the pro-genitor star departs from the AGB after the end of mass loss episodes,its envelope is made up of a mixture of hy-drogen and helium.Also,in deeper layers and below the nearly pure helium buffer,there is an underlying region rich in both helium and carbon(see next section);thus the use of the trace element approximation would not be appropriate for our purposes.In this study we are interested in the chem-ical evolution occurring quite deep in the star,thus radiative levitation and possible wind mass loss from the surface dur-ing the hot white dwarf stages,which are expected to alter the surface composition of these stars,have been neglected (see Unglaub&Bues2000for a recent detailed study of the evolution of chemical abundances in surface layers of hot white dwarfs).In the context of white dwarf evolution,the treatment for diffusion we use here has been employed by Iben&MacDonald(1985,1986)(thermal diffusion not in-cluded).Recently,it was applied by MacDonald,Hernanz &Jos´e(1998)to address the problem of carbon dredge-up in white dwarfs with helium-rich envelopes and by Althaus, Serenelli&Benvenuto(2001a,b)to explore the role played by diffusion in inducing thermonuclearflashes in low-mass, helium-core white dwarfs.Details about the procedure we follow to solve the dif-fusion equations are in Althaus&Benvenuto(2000).In par-ticular,we follow the evolution of the isotopes1H,3He,4He, 12C,14N and16O.In order to calculate the dependence ofthe structure of our white dwarf models on the diffusively evolving abundances self-consistently,the set of equations describing diffusion has been coupled to our evolutionary code.After computing the change of abundances by effect of diffusion,they are evolved according to the requirements of nuclear reactions and convective mixing.Finally,we empha-size that radiative opacities during the white dwarf regime are calculated for metallicities consistent with the diffusion predictions.In particular,the metallicity is taken as two times the abundances of CNO elements as suggested by Iben &MacDonald(1986).3EVOLUTIONARY RESULTS3.1White dwarf progenitorHere we describe the results we obtained with regard to the evolutionary phases prior to the white dwarf formation.We shall limit ourselves to describe the main features of such evolution particularly those which are of immediate rele-vance for the white dwarf formation,and we refer the reader to the works of Mazzitelli&D’Antona(1986),Vassiliadis& Wood(1993),Bl¨o cker(1995a)amongst others for a more complete description about the evolution of low and inter-mediate mass stars.We begin by examining the complete evolutionary track in the Hertzsprung-Russell diagram that is illustrated in Fig.1.Our numerical simulation covers all the evolutionary phases of an initially3M⊙star from the ZAMS to the domain of ZZ Ceti stars on the white dwarf cooling branch.The age(in units of104yr)from the end of mass loss episodes and the mass of hydrogen(in units of 10−4M⊙)are indicated at selected points along the track. For clarity,the evolutionary phases corresponding to mass loss are not plotted.After4.1×108yr of evolution and by the end of helium burning in the core,thefirst feature worthy of comment predicted by our calculations is the appearance of a series of micro-pulses(not to be confused with the major thermal pulses on the AGB)of low amplitude in the surface lumi-nosity.Such micro-pulses are due to thermal instabilities in the helium-burning shell above the carbon-and oxygen-rich core,which causes the helium luminosity to undergo oscillations.Specifically,such pulses appear when the cen-tral helium abundance by mass falls below≈0.001(and the convective core vanishes).The time dependence of the sur-face luminosity L∗and the helium-burning luminosity L He (in solar units)during the micro-pulse phase is shown in two insets in Fig.1,where the time scale is given in million years from the ZAMS.A total of40micro-pulses with an inter-pulse period of≈3.1×105yr occurred.Note that the pulse amplitude in the surface luminosity is indeed modest (∆Log(L/L⊙)≈0.02at most).It is worth mentioning that thermal micro-pulses occurring in a3M⊙star towards the end of its core helium-burning phase have also been reported by Mazzitelli&D’Antona(1986).After the end of micro-pulses,the star evolves until complete helium exhaustion at the centre.The total time spent during central helium burning amounts to about1.25×108yr.After helium is exhausted in the core,leaving a central oxygen abundance of0.62by mass,evolution proceeds to-wards the phase of the major thermal pulses on the AGB, at which point helium shell burning becomes unstable again. The AGB evolution of intermediate-mass stars is well known to be characterized by helium shellflashes during which the burning rate rises very steeply.In our simulation,the time elapsed from central helium exhaustion until thefirst ther-mal pulse is2.6×107yr,when the surface luminosity exceeds Log(L/L⊙)=3.2for thefirst time in its evolution.After ex-periencing11thermal pulses and considerable mass loss,the mass of the hydrogen envelope is reduced so much that the star departs from the AGB and evolves towards large effec-tive temperatures.This takes place when the star luminosity is supported by stationary helium burning.We will discuss the implications of this situation later in this section,for now suffice it to say that when mass loss ends,the remnant con-sumes a considerable fraction of its remaining hydrogen in a redward“hook”on the Hertzsprung-Russell diagram.Dur-ing this phase,evolution proceeds very slowly .As a result of mass loss episodes,the stellar mass has been decreased from3to0.563M⊙.Eventually,the remnant reaches the white dwarf cooling branch.Thereafter,element diffusion alters the chemical abundance distribution within the star even at the lowest computed luminosity stages.During the white dwarf cooling phase,the coupled effects of hydrogen burning and element diffusion reduce the mass of hydrogen that is left in outer layers by almost a factor of2.The time dependence of the surface luminosity duringWe want to mention that we have not considered further mass loss after the star has reached log T eff=3.8for thefirst time after leaving the AGB.c 2001RAS,MNRAS000,1–11Evolution of a3M⊙star from the main sequence to the ZZ Ceti stage5the thermally pulsing phase is detailed in the upper panel of Fig.2,where the time scale is given in million years counted from the ZAMS.A total of11thermal pulses have been computed before the white dwarf progenitor departs from the AGB.This phase of evolution has been studied in detail by numerous authors in the literature(Sch¨o nberner1979; Iben1982;Iben&Renzini1983;Vassiliadis&Wood1993 amongst others)and we refer the reader to those studies for details.Let us however mention some words about the role played by various relevant luminosities by the time the star is next to evolve away from the AGB towards the white dwarf state.To this end,we show in the lower panel of Fig.2the evolution of the surface luminosity(L∗)and the hydrogen-and helium-burning luminosities(L H and L He respectively) during and between the tenth and eleventh pulses.Depar-ture from the AGB could in principle occur at different stages during the inter-pulse.Here,we will direct our attention to one particular sit-uation:that in which the star leaves the AGB during the quiescent helium-burning phase following the eleventh he-lium thermal pulse.Our simulation is thus representative of the possibility that departure from the AGB takes place early in the helium shellflash cycle.The consequence for the post-AGB evolution resulting from departure at different lo-cations on the inter-pulse has been carefully explored by nu-merous investigators,amongst them Iben(1984),Wood& Faulkner(1986),Bl¨o cker(1995b).Such studies show for in-stance that the transition time from AGB to the planetary nebula region depends strongly on the phase at which the star leaves the AGB.From the bottom panel of Fig.2we see that the star departs from the AGB when helium shell burning is dominant.Specifically,the helium-burning shell contributes82%of the surface luminosity by the time the ef-fective temperature begins to increase.In the meantime the hydrogen shell is almost extinguished.It is worthwhile to comment that helium-burning luminosity in the shell source reaches5×106L⊙,causing an expansion in the layers above with the consequence that hydrogen burning decreases sig-nificantly to be almost extinguished and leading to a sharp spike in the surface luminosity.After that,helium luminosity begins to drop and hydrogen is re-ignited.For the sake of completeness,we show in Fig.3the behaviour of the central conditions during the whole evo-lution from the hydrogen burning in the core on the main sequence to the white dwarf state.Relevant episodes in the life of the star are indicated in thefigure.In particular, the response of the central region to the occurrence of both thermal pulses and micro-pulses is noted.Once the remnant leaves the AGB,evolution proceeds at almost constant cen-tral density to become a white dwarf.3.2Post-AGB and white dwarf evolutionAfter the end of the thermally pulsing phase,the remnant star departs from the asymptotic giant branch at low effec-tive temperature and evolves as a planetary nebula nuclei towards higher effective temperatures.In Fig.4we show as a function of effective temperature the mass of hydro-gen in outer layers(in units of10−3M⊙)for the0.563M⊙post-AGB remnant from a stage in the evolution just before the end of mass loss till that corresponding to the ZZ Ceti domain in the white dwarf regime.Numbers in parenthesis besides circles at selected points on the curve give the age in years counted from the end of mass loss and the contribution of the helium shell burning to surface luminosity.By the end of mass loss(at log T eff=3.8)the contribution of the helium shell burning to surface luminosity has been reduced to55 %.Thereafter,the remnant star returns to the AGB and in-creases its surface luminosity up to the inter-flash maximum value.During this phase,helium burning becomes less im-portant and the hydrogen content in outer layers is reduced, as a result of increasing hydrogen burning,from≈2×10−3 M⊙at the end of mass loss down to≈5×10−4M⊙once the remnant resumes its evolution to the blue.By the time the mass of the hydrogen content decreases below≈8×10−4 M⊙,helium burning becomes virtually extinct and hydro-gen burning via CN cycle reactions becomes the dominant source of surface luminosity.It is worth noting that evolu-tion proceeds very slowly during this phase and the remnant star spends a substantial fraction of its post-AGB transition time there(about46000yr).Note also that the star takes about48000yr to reach an effective temperature of30000K required for the excitation of the planetary nebula.This time is so long that no planetary nebula is produced.These re-sults qualitatively resemble those of Mazzitelli&D’Antona (1986),who found that if departure from the AGB takes place during the quiescent helium burning phase,then,when mass loss is stopped,the remnant spends a considerable time in consuming most of its hydrogen envelope as a red super-giant.Long post-AGB evolutionary time scales were also found by Wood&Faulkner(1986)when their models are forced to abandon the AGB early in the inter-pulse phase. As well known,post-AGB times are strongly dependent on the phase of the helium shellflash cycle at which the star leaves the AGB.In this regard,had our white dwarf pro-genitor been forced to depart from the AGB somewhat later than assumed here while burning hydrogen(by employing a smaller mass loss rate),it would not have returned to the AGB⋆⋆and its further evolution would thus have proceeded much faster(see Mazzitelli&D’Antona1986and Wood& Faulkner1986).Notefinally that the mass of hydrogen that is left in outer layers at the start of the cooling branch is about1.5×10−4M⊙,and this is reduced to7×10−5M⊙by the time the ZZ Ceti domain is reached.Because we have not invoked additional mass loss episodes during the planetary nebula stage or early during the cooling branch,the quoted value for thefinal hydrogen mass should be considered as an upper limit.We stress that in the present calculation we have adopted an initial metallicity of Z=0.02;much lower values of Z would give rise to a largerfinal hydrogen enve-lope mass for the same stellar mass(see for instance Iben& MacDonald1986).Since the chemical stratification of the white dwarf is relevant for our purposes,let us detail the resulting chemical profile of the post-AGB remnant.In particular,the carbon and oxygen abundance distribution within the core of the remnant is detailed in Fig.5.The inner part of the core ⋆⋆Should departure have occurred very late in the pulse cycle, then a last helium shellflash would be expected to occur in the planetary nebula nuclei stage or even in the white dwarf regime, thus giving rise to a born-again AGB star(Sch¨o nberner1979; Iben1984).c 2001RAS,MNRAS000,1–11。